Apparatus for providing controlled cooling of thermoplastic strands

Abstract

Apparatus is provided for controlled cooling of thermoplastic strands between the time that they are extruded from a melt of thermoplastic material until they are cut into pellets by a pelletizer that pulls the strands into it. A first tray inclined downwardly from the extruder receives the strands which are sprayed with cooling liquid while in the tray. A second tray inclined upwardly from the bottom of the first tray toward the pelletizer receives the strands which are also sprayed while in the second tray. Cooling liquid is also introduced at the inlet end of the first tray. A gravity liquid removal screen is positioned at the low point of each tray to remove the cooling liquid from the trays. A vacuum system for removing cooling liquid from the strands may also be positioned between the higher end of the second tray and the pelletizer. The temperature and quantity of the cooling liquid sprayed on the first tray, that sprayed on the second tray, and that introduced at the inlet end of the first tray are individually controlled by a cooling liquid control system utilizing a programmable central micro-processor.

We claim: 
     
       1. Apparatus for providing controlled cooling of thermoplastic strands as they move to a pelletizer comprising: a first inclined tray receiving a plurality of side-by-side thermoplastic strands as said strands are discharged from an extruder, said first inclined tray being inclined downwardly away from said extruder;   a second inclined tray in end-to-end relationship with said first inclined tray and extending upwardly from the lower end of said first inclined tray toward said pelletizer;   hold down means at the intersection of said first and second trays to position said strands in said trays as said strands move down said first tray and then up said second tray;   a pelletizer having means to pull thermoplastic strands through said first and second trays into said pelletizer where said pelletizer cuts said strands into pellets;   a first plurality of cooling liquid sprays to spray cooling liquid onto said strands as they pass through said first tray;   a second plurality of cooling liquid sprays to spray cooling liquid onto said strands as they pass through said second tray;   said first plurality of sprays and said second plurality of sprays each utilizing cooling liquid whose temperature is independently controlled by a cooling liquid control system; and   gravity cooling liquid removal means located in the low ends of said first and second inclined trays.   
     
     
       2. The apparatus of claim 1 wherein cooling liquid is introduced into said first tray below said strands and the temperature of said cooling liquid is independently controlled by said cooling liquid control system. 
     
     
       3. The apparatus of claim 2 wherein said cooling liquid is water. 
     
     
       4. The apparatus of claim 1 wherein the angle of inclination from horizontal of said first tray is from 3° to 15°, inclusive. 
     
     
       5. The apparatus of claim 1 wherein the angle of inclination from horizontal of said second tray is from 3° to 15°, inclusive. 
     
     
       6. The apparatus of claim 1 wherein said cooling liquid control system comprises a central micro-processor to control the temperature and quantity of cooling liquid emitted by said first plurality of cooling liquid sprays and by said second plurality of cooling liquid sprays. 
     
     
       7. The apparatus of claim 1 wherein said thermoplastic strands pass over means for providing an air stream to remove cooling liquid from said strands after leaving said second tray and before entering said pelletizer. 
     
     
       8. The apparatus of claim 1 wherein said first inclined tray is substantially wider at its inlet end where it receives said thermoplastic strands than at its outlet end where it joins to said second inclined tray. 
     
     
       9. The apparatus of claim 1 wherein said first plurality of cooling liquid sprays spray cooling liquid onto said strands in a direction substantially perpendicular to the movement of said strands and said second plurality of cooling liquid sprays spray cooling liquid onto said strands at an angle opposing the direction of travel of said strands in said second inclined tray. 
     
     
       10. Apparatus for providing controlled cooling of thermoplastic strands as they move to a pelletizer comprising: a first inclined tray receiving a plurality of side-by-side thermoplastic strands as said strands are discharged from an extruder, said first inclined tray being inclined downwardly away from said extruder at an angle of from 3° to 15°, inclusive, from the horizontal;   a second inclined tray in end-to-end relationship with said first inclined tray and extending upwardly from the lower end of said first inclined tray toward said pelletizer at an angle of from 3° to 15°, inclusive, to the horizontal;   hold down means at the intersection of said first and second trays to position said strands in said trays as said strands move down said first tray and then up said second tray;   a pelletizer having means to pull said thermoplastic strands through said first and second trays into said pelletizer where said pelletizer cuts said strands into pellets;   a first plurality of cooling liquid sprays to spray cooling liquid onto said strands as they pass through said first tray;   a second plurality of cooling liquid sprays to spray cooling liquid onto said strands as they pass through said second tray;   means for introducing cooling liquid into said first tray below said strands;   said first plurality of sprays, said second plurality of sprays, and said means for introducing cooling liquid into said first tray each utilizing cooling liquid whose temperature is controlled independently by a cooling liquid control system;   gravity cooling liquid removal means located in the low ends of said first and second inclined trays; and   means located between said second inclined tray and said pelletizer for providing an air stream to remove cooling liquid from said strands.   
     
     
       11. The apparatus of claim 10 wherein said cooling liquid is water. 
     
     
       12. The apparatus of claim 10 wherein said cooling liquid control system comprises a central micro-processor to control the temperature and quantity of cooling liquid emitted by said first plurality of cooling liquid sprays, by said second plurality of cooling liquid sprays, and by said means for introducing cooling liquid into said first tray. 
     
     
       13. The apparatus of claim 10 wherein said first inclined tray is substantially wider at its inlet end where it receives said thermoplastic strands than at its outlet end where it joins to said second inclined tray. 
     
     
       14. The apparatus of claim 10 wherein said first plurality of cooling liquid sprays spray cooling liquid onto said strands in a direction substantially perpendicular to the movement of said strands and said second plurality of cooling liquid sprays spray cooling liquid onto said strands at an angle opposing the direction of travel of said strands in said second inclined tray. 
     
     
       15. The apparatus of claim 10 wherein said means for providing an air stream to remove cooling liquid from said strands comprises a screen supporting said strands with a vacuum pump creating a reduced atmospheric pressure below said screen whereby air flows from above said strands to the area of reduced pressure below said screen. 
     
     
       16. Apparatus for providing controlled cooling of thermoplastic strands as they move to a pelletizer comprising: a first inclined tray receiving a plurality of side-by-side thermoplastic strands as said strands are discharged from an extruder, said first inclined tray being inclined downwardly away from said extruder at an angle of from 3° to 15°, inclusive, from the horizontal and being substantially wider at its inlet end where it receives said thermoplastic strands than at its lower end;   a second inclined tray in end-to-end relationship with said first inclined tray and extending upwardly from the lower end of said first inclined tray toward said pelletizer at an angle of from 3° to 15°, inclusive, to the horizontal;   hold down means at the intersection of said first and second trays to position said strands in said trays as said strands move down said first tray and then up said second tray;   a pelletizer having means to pull said thermoplastic strands through said first and second trays into said pelletizer where said pelletizer cuts said strands into pellets;   a first plurality of water sprays to spray water onto said strands as they pass through said first tray, said first plurality of water sprays spraying water on said strands in a direction substantially perpendicular to the movement of said strands;   a second plurality of water sprays to spray water onto said strands as they pass through said second tray, said second plurality of water sprays spraying water on said strands at an angle opposing the direction of travel of said strands;   means for introducing water into said first tray below said strands;   said first plurality of sprays, said second plurality of sprays, and said means for introducing water into said first tray each utilizing water whose quantity and temperature are controlled independently by a water control system, said water control system including a central microprocessor;   a gravity water removal screen located in the low ends of said first and second inclined trays; and   a screen supporting said strands between said second inclined tray and said pelletizer with a vacuum pump creating a reduced atmospheric pressure below said screen whereby air flows from above said strands to the area of reduced pressure below said screen thereby removing water from said strands.   
     
     
       17. The apparatus of claim 16 wherein said water control system comprises: a water reservoir;   first water delivery conduits to deliver water from said reservoir to said first plurality of sprays;   second water delivery conduits to deliver water from said reservoir to said second plurality of sprays;   third water delivery conduits to deliver water from said reservoir to said means for introducing water to said first tray;   separately controllable heat exchangers located in each of said first, second and third delivery conduits;   separately controllable heaters located in each of said first, second and third delivery conduits;   separately controllable water quantity control valves located in each of said first, second and third delivery conduits to control the quantity of water flowing therethrough;   separate temperature responsive thermocouples located in said first, second and third delivery conduits to determine the water temperature therein;   said central micro-processor being programmable to control individually said heat exchangers, said heaters and said water quantity control valves to control the temperature of the water in response to said thermocouples and to control the quantity of water flowing through each of said first, second and third delivery conduits by controlling said water quantity control valves.   
     
     
       18. The apparatus of claim 17 wherein said heat exchangers receive cooling water through valves that are controlled by said central micro-processor. 
     
     
       19. The apparatus of claim 17 wherein water is returned to said water reservoir after it passes through said gravity water removal screen. 
     
     
       20. The apparatus of claim 17 wherein water is returned to said water reservoir after it is drawn through said screen between said second tray and said pelletizer.